JPH062008A - Method for centrifugally forming metal powder compact - Google Patents

Abstract

PURPOSE:To form a good-quality metal powder compact having a long-sized tube shape, etc., which has not been attained by the compaction using a die, etc. CONSTITUTION:A metallic mold 10 pierced dispersely with liq. discharge holes 11 is lined with a water-permeable sheet 12 to costitute a forming mold, the mold is horizontally placed on a rotating device such as a turning roller 20, and a slurry S of metal powder is injected into the mold. The slurry S is pressed on the inner mold surface in layers by the centrifugal force due to the rotation of the mold, the water in the slurry is discharged to the outside from the holes 11, and the depositing layer of metal grains is formed on the inner mold surface (water-permeable sheet surface). The depositing layer is compacted and densified by the centrifugal force, and a homogeneous and highly dense metal powder compact is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for molding a metal powder compact which is subjected to a sintering process for producing a sintered metal member.

[0002]

2. Description of the Related Art A method for producing a metal member (sintered body) by a powder metallurgy method in which a powder compact having a required shape is formed by using a metal powder adjusted to have a required chemical composition as a raw material and sintered Compared with the manufacturing method by melting / casting process,
It has a high degree of freedom in the design of alloy composition, and it is also possible to manufacture member products of materials that are difficult or impossible by the melting / casting method. It has advantages that various kinds of defects are not accompanied and a homogeneous member with less segregation can be manufactured with a relatively high yield. In the production of a sintered metal member, the forming step of the metal powder compact prior to the sintering step is
This is an important process that affects the quality of the sintered product, and the typical forming method is to fill the die with metal powder, punch,
Pressure molding method that compresses and densifies with a plungeer, hydrostatic isotropic pressure molding method that compresses and densifies a rubber mold with metal powder and uses a fluid as a pressure medium, prepares a kneaded product of metal powder, and performs extrusion molding, etc. The plastic forming method and the like for carrying out are carried out industrially.

[0003]

However, in the pressure molding method using a die, a large friction is generated at the interface between the die and the filling powder, and the particles are cross-linked by friction or entanglement during the powder compression process. Therefore, the transmission of high pressure force to the central part is hindered, and in a thick and large diameter molded body,
There are drawbacks such as unevenness in density between the surface layer and the inside being large, and it is also difficult to mold a long-sized molded body such as a tubular body. The hydrostatic isotropic pressure molding method, unlike the pressure molding method using the above-mentioned mold, does not involve a partial pressure difference, and can apply a pressing force uniformly to the entire surface, but requires a special device, In addition to being extremely costly, it is often impossible to perform molding of large diameter and long size such as pipes due to restrictions on the facility capacity. In a plastic molding method such as extrusion molding, since it is necessary to give a kneaded product sufficient moldability, a large amount of binder must be blended, so it is difficult to make the product highly densified. It is also difficult to form large diameter and long size. Therefore, the present invention provides a large-diameter long-sized size without requiring special equipment, even with a large-sized size, without unevenness in density between the surface layer and the inside, and regardless of its shape and size. Another object of the present invention is to provide a molding method excellent in practicability, which can efficiently mold a metal powder compact having a uniform and high density.

[0004]

A method for molding a metal powder compact according to the present invention is a molding mold in which a water-permeable sheet is lined on the inner surface of a mold having dispersed drainage holes formed on the inner surface. Then, the slurry in which the metal powder is suspended is injected, and the dispersion medium of the slurry in the mold is discharged to the outside from the drain hole under the action of the centrifugal force due to the rotation of the molding mold, and at the same time, the inner surface of the mold is compressed and dense. It is characterized by forming a metalized metal particle deposition layer.

[0005]

According to the present invention, a suspension of metal powder is used as a raw material to centrifugally mold a metal powder compact, and the slurry of the metal powder injected into the molding mold is molded by centrifugal force generated by rotation of the mold. A uniform layer is formed along the inner surface of the mold and pressed, water is separated and removed from the slurry layer, and metal particles are deposited and deposited on the inner surface of the mold. Centrifugal force acts as a force that presses the metal particles that have been deposited and accumulated on the inner surface of the mold toward the inner surface of the mold.
The particle deposition layer is compressed and densified. By increasing the rotational speed of the mold and increasing the centrifugal force, the compactness is further increased,
A target metal powder compact is obtained as the particle deposition layer. As described above, in the present invention, the centrifugal force due to the rotation of the molding mold acts as a pressing force of the metal particles against the inner surface of the mold, and since the molded body is molded as a deposition layer of particles, the powder filled in the pressing mold Unlike a compression densification mechanism such as a pressure molding method in which a compressive force is applied from the surface of the layer, there is almost no friction between particles, formation of a crosslink, and unevenness of coarse and dense due to this, even if it is a thick wall size. ,
It is possible to form the moldability which is excellent in the dense homogeneity in the layer thickness direction.

Further, since the size of the molding mold used in the centrifugal molding operation of the present invention is not substantially limited,
It is also possible to mold a molded body having a large diameter and long tube shape.
That is, the centrifugal force caused by the rotation of the molding mold acts uniformly on the slurry in the mold over the entire circumference,
Since metal particles uniformly deposit and accumulate centrifugal force as a pressing force against the inner surface of the mold, they have a large-diameter, long-sized and thick-walled tubular shape that cannot be formed by a pressure forming method using a pressing die. Even a molded product can be obtained as a molded product having a uniform and high density over the entire circumference.

The present invention will be described in detail below. Metal powder suspension slurry used in the centrifugal molding of the present invention,
Metal powder adjusted to a predetermined chemical composition, added to water or an appropriate organic solvent, if necessary, a binder, a dispersant,
It is prepared by adding a plasticizer, a viscosity modifier, a surface active agent, an antifoaming agent, an antirust agent, etc., adjusting the pH, and uniformly stirring and mixing. The particle size of the metal powder is, for example, an average particle size of 10 μm, and the slurry concentration can be, for example, 75% (solid content concentration). FIG. 1 shows an example of forming a tubular shaped body by horizontal centrifugal molding as an embodiment of the present invention. Reference numeral 10 is a mold mold, 11 is a drainage hole that opens on the inner surface of the mold mold 12, and 12 is a water-permeable sheet lined on the inner surface of the mold mold. The drainage holes 11 are holes for discharging the moisture of the slurry of the metal powder injected into the mold 10 to the outside, and are formed dispersed in the circumferential direction and the axial direction of the mold 10. Water-permeable sheet 12
The metal particles in the slurry are drain holes 11 of the mold 10.
To prevent discharge from the slurry, to serve as a filter medium for permeating and discharging only the slurry moisture, and to facilitate the demolding work when extracting the centrifugally molded metal powder compact in the mold. A sheet having a mold action and having an appropriate mesh and strength is used.

Reference numeral 20 denotes a turning roller, and the mold die 10 has a turning roller 2 with its axis centered horizontally.
It is carried on 0. The turning roller 20 transmits the rotation of a variable speed motor or the like (not shown) connected to the turning roller 20 to the die mold 10 and causes the die mold 10 to rotate about its horizontal axis. Reference numeral 30 denotes a slurry hopper, which injects the metal powder slurry S into the mold 10 through the opening 14 of the end plate 13 fitted to the opening end of the mold 10.

The slurry S of the metal powder injected from the hopper 30 into the mold 10 flows and diffuses along the inner surface of the mold 10 by the rotary motion of the mold 10.
Due to the action of centrifugal force, it is pressed in a uniform layer over the entire length of the inner surface of the mold. Under the action of the centrifugal force, the water content of the slurry permeates the water permeable sheet 12 and is discharged to the outside through the drainage holes 11, and at the same time, a deposition layer of metal particles is formed on the inner surface of the mold 10. As a compression effect of the particle deposition layer by the centrifugal force in the centrifugal molding (for example, gravity multiple G _NO about 20 to 30), a dense and homogeneous molded body can be obtained.

Initially, the mold mold 10 is rotated at a slow rotation speed within a range where the rain fall phenomenon of the slurry (dripping from the ceiling side of the inner surface of the mold) does not occur.
By gradually controlling the rotation speed to be high speed, even if the particle size distribution width of the metal powder used is relatively large, the separation of the specific gravity of the metal particles due to the difference in the particle size is suppressed and prevented,
It is possible to obtain a molded product with less deviation in the particle size distribution in the thickness direction. Also, after the water content of the slurry has been eliminated to the extent that particles do not float, the centrifugal force is further increased to make the particle deposition layer more dense and dense without impairing the uniformity of the particle size distribution. You can After a predetermined particle deposition layer (molded body) is formed in the mold 10, the rotation of the mold is decelerated and stopped, and the end plate 1 at the opening end of the mold 1 is formed.
3 is removed, and the molded body is demolded. At the time of demolding, the water-permeable sheet 12 facilitates demolding of the molded body by the releasing action,
Effective in preventing damage and deformation of the molded body.

In the above description, horizontal centrifugal molding was taken as an example, but depending on the shape and size of the desired metal powder compact,
If it is convenient to perform vertical centrifugal molding in which the molding mold is erected and fixed on the rotary table and the vertical axis is the center of rotation, instead of horizontal centrifugal molding, this may be done.

The metal powder compact molded by the centrifugal molding method of the present invention is demolded from the mold, dried and degreased at room temperature or under heating, and then subjected to a sintering step and treated in a conventional manner. The final product is a sintered metal product.

[0013]

EFFECTS OF THE INVENTION According to the present invention, a pressure molding method using a pressing die, a hydrostatic isostatic pressure molding method, or a plastic molding method, such as a metal powder molding having a large diameter, thick wall and a long tube shape, etc. According to the method or the like, even those having a shape or size that is difficult or impossible to mold can be easily molded. No special device is required to carry out the centrifugal molding operation of the present invention, and a molding mold having a shape size corresponding to a molded body to be molded, and a rotation driving device such as a turning roller or a rotary table for rotating the molding mold. It can be implemented with a simple device configuration consisting of, is highly practical, and is extremely advantageous in terms of cost. Since the metal powder compact according to the present invention is formed under the action of centrifugal force, it has less unevenness in density, is uniform and has excellent compactness, and has significantly less strain and residual stress derived from the molding process. Due to the homogeneity and high density of this molded body, the quality characteristics such as mechanical strength of the sintered product are improved, and since it is homogeneous and has less distortion and residual stress, there is less occurrence of thermal deformation such as bending during the sintering process. Further, it is possible to obtain effects such as a reduction in finishing machining cost, a reduction in processing cost, and an improvement in manufacturing yield.

[Brief description of drawings]

FIG. 1 is an explanatory sectional view showing an embodiment of a centrifugal molding method of the present invention.

[Explanation of symbols]

10: Mold for molding, 11: Drainage hole, 12: Water-permeable sheet, 13: End plate, 20: Turning roller, 30: Slurry hopper, S: Metal powder suspension slurry.

Claims (1)

[Claims] 1. A molding mold in which a slurry in which a metal powder is suspended is poured into a molding mold in which a water-permeable sheet is lined on the inner surface of a die mold in which drain holes opening on the inner surface are dispersed. The dispersion medium of the slurry in the mold is discharged to the outside from the drain hole under the action of the centrifugal force due to the rotation of the metal, and a metal particle deposition layer that is compressed and densified is formed on the inner surface of the mold. A method for centrifugally molding a powder compact.